This invention relates to aminopropylated aromatic amines, more particularly to N-(aminopropyl)-ortho-toluenediamine, N-(aminopropyl)-meta-toluenediamine and their use as epoxy curing agents.
It is known to use amines, such as aliphatic or aromatic amines, for the curing of epoxy resins. See, e.g., xe2x80x9cHandbook of Epoxy Resinsxe2x80x9d by H. Lee and K. Neville, McGraw Hill Book Co., 1967. The epoxy industry, particularly the adhesive, composite and syntactic foam markets of the industry, is in need of a low viscosity aromatic amine curing agent fairly rapid in reactivity and heat generation while providing high Tg, good fracture toughness and chemical resistance after full cure. Additionally, the civil engineering epoxy market has particular interest in finding new amine curatives that combine the rapid curing rate of aliphatic amines with the good chemical resistance typically found in aromatic amine curatives, such as MDA and DETDA.
Low viscosity amine curing agents are typically aliphatic amines, cycloaliphatic amines or amidoamines. These amine curatives provide the appropriate viscosity and in some cases adequate fracture toughness for adhesive, composite and syntactic foam applications, but are not suitable for many applications in that they are too reactive and do not provide high Tg and good chemical resistance. For civil engineering applications, these amine curatives sometimes have the appropriate reactivity and viscosity, but do not provide adequate chemical resistance. Aromatic amines, on the other hand, provide high Tg, good fracture toughness and excellent chemical resistance for adhesive, composite and syntactic foam applications but are less than ideal in that they are usually high viscosity liquids or solids, have extremely long potlifes and high toxicity. For civil engineering applications aromatic amine curatives provide good chemical resistance but are slow in reactivity and present toxicity issues as well.
The epoxy industry has employed many types of curative blends in an attempt to maximize the desired application properties, but in most cases at the expense of other properties. Additives such as accelerators, tougheners, reactive diluents and non-reactive diluents are employed to maximize a desired property but again to the deterioration of other properties. A number of good references are available on this subject including: Lee and Neville""s, xe2x80x9cHandbook of Epoxy Resins,xe2x80x9d cited above, and W. R. Ashcroft, xe2x80x9cCuring Agents for Epoxy Resins,xe2x80x9d in B. Ellis (ed.). xe2x80x9cChemistry and Technology of Epoxy Resins,xe2x80x9d Blackie Academic and Professional, London (1993), pp. 37-73.
Others in the epoxy industry have developed novel amines in attempting to optimize curative properties. For example, Japanese Patent 2963739 (1999) describes the use of substituted-N-phenyl-1,3-propanediamines as liquid epoxy curatives which do not B-stage during cure and thus yield a fully cured epoxy resin. The substituted-N-phenyl-1,3-propanediamines described therein are represented by the following chemical formula: 
where R is hydrogen, lower alkyl group, lower alkoxyl group or halogen. Although the method of synthesis of these curatives is not disclosed, other references teach methods for synthesizing aromatic amines.
For example, European Patent 0 067 593 (1982) describes the cyanoethylation of para, meta, and ortho phenylenediamine to generate 3,3xe2x80x2-(p,m or o-phenylenedi-imino)-dipropanenitrile: 
EP 0 067 593 teaches the use of water as the solvent and concentrated hydrochloric acid as the catalyst to obtain the dicyanoethylated product.
Elderfield et al., 68 J. Amer. Chem. Soc. 1262 (1949), describes the synthesis of xcex2-p-anisidinopropionitrile by boiling p-anisidine and acrylonitrile in acetic acid.
Cookson et al., xe2x80x9cThe Cyanoethylation of Amines and Arsines,xe2x80x9d J. Chem. Soc. 1949, pp. 67-72, describes the cyanoethylation of aniline by heating to 150xc2x0 C. a mixture of aniline and acrylonitrile in the presence of excess acetic acid in an autoclave to generate 2-cyanoethylaniline and bis-2-cyanoethylaniline. The reference further describes the reaction of diphenylamine and acrylonitrile in an excess of acetic acid using a catalytic amount of fine copper powder to generate diphenyl-2-cyanoethylamine.
Braunholtz et al., xe2x80x9cThe Preparation of Bis(2-cyanoethyl) Derivatives of Aromatic Primary Amines, and Their Conversion into 1:6-Diketojulolidines,xe2x80x9d J. Chem. Soc., 1952, pp. 3046-3051, describes the cyanoethylation of aniline, m-toluidine, p-toluidine, p-anisidine and p-chloroaniline in an excess of acetic acid.
Braunholtz et al., xe2x80x9cThe Preparation of Bis(2-cyanoethyl) Derivatives of Aromatic Primary Amines, and Their Conversion into 1:6-Diketojulolidines. Part II,xe2x80x9d J. Chem. Soc., 1953, pp. 1817-1824, describes the cyanoethylation of several different aromatic primary monoamines in an excess of acetic acid using various metal catalysts to selectively generate mono and di-cyanoethylated derivatives.
All references cited herein are incorporated herein by reference in their entireties.
The invention provides aminopropylated toluenediamines, processes for synthesizing them, compositions containing them and methods for using them to cure epoxy resins. In preferred embodiments, the aminopropylated toluenediamines are represented by the following formula: 
where the nitrogen atoms are ortho or meta to each other on the aromatic ring.
With regard to the present invention and throughout the specification and claims the terms xe2x80x9caminopropyl toluenediamine(s)xe2x80x9d, xe2x80x9caminopropylated toluenediamine(s)xe2x80x9d, xe2x80x9cN-(aminopropyl) toluenediamine(s)xe2x80x9d and xe2x80x9cN-(aminopropylated) toluenediamine(s)xe2x80x9d are used interchangeably.
The most preferred aminopropylated toluenediamines of the invention are suitable for use as epoxy resin curing agents. Aminopropylated toluenediamines where the nitrogen atoms are ortho or meta to each other on the aromatic ring have been found to be particularly suitable for this purpose. Thus, the most preferred aminopropylated toluenediamines of the invention are aminopropylated products of ortho-toluenediamine represented by the following Formulas I-IV: 
and aminopropylated products of meta-toluenediamine represented by the following Formulas V-VII: 
Formulas I-IV above are the aminopropylated products of ortho-toluenediamine (OTD). Formulas I-II are based on 2,3-toluenediamine (TDA) and the Formulas III-IV are based on 3,4-TDA. A commercial isomer mix of OTD is typically 60/40 2,3-TDA/3,4-TDA. Using commercial grade OTD therefore leads to aminopropylated isomer mixtures.
Formulas V-VII above are the aminopropylated products of meta-toluenediamine (MTD). Formula V is based on 2,6-TDA and Formulas VI and VII are based on 2,4-TDA.
Aminopropylated products of OTD are prepared by two reaction steps. As shown in Equations I and II (below), OTD is initially cyanoethylated by reaction with acrylonitrile (ACN) at elevated temperature in the presence of an acid and a protic solvent (e.g., water) for a period of time adequate for reaching the desired extent of conversion to the cyanoethylated product. The resulting cyanoethylated TDA is then hydrogenated under pressure (e.g., 900 psi or 6.21 Mpa) and temperature using a hydrogenation catalyst (e.g., Raney cobalt or nickel). The resulting aminopropylated TDA is then purified by reduced pressure fractional distillation.
Cyanoethylation of Orthotoluenediamine (Eq. I) 
Hydrogenation of Cyanoethylated Orthotoluenediamine (Eq. II) 
Aminopropylated products of MTD are prepared by two reaction steps. As shown in Equations III and IV, MTD is initially cyanoethylated by reaction with ACN at elevated temperature in the presence of an acid and a protic solvent (e.g., water) for a period of time adequate for reaching the desired extent of conversion to the cyanoethylated product. The resulting cyanoethylated TDA is then hydrogenated under pressure (e.g., 900 psi or 6.21 Mpa) and temperature using a hydrogenation catalyst (e.g., Raney cobalt or nickel). The resulting aminopropylated TDA is then purified by reduced pressure fractional distillation.
Cyanoethylation of Metatoluenediamine (Eq. III) 
Hydrogenation of Cyanoethylated Metatoluenediamine (Eq. IV) 
In the preparation of aminopropylated OTD, either the pure compounds 2,3-TDA or 3,4-TDA, or isomer mixtures, such as 60/40 2,3-TDA/3,4-TDA, can be reacted with ACN. In fact, any blend or mixture of the TDA isomers may be used. The preferred reactant mixture comprises commercial grade OTD.
In the preparation of aminopropylated MTD, either the pure compounds 2,4-TDA, 2,6-TDA, or isomer mixtures such as 80/20 2,4-TDA/2,6-TGA can be reacted with ACN. Any blend or mixture of the TDA isomers can be used. The preferred reactant mixture comprises commercial grade MTD.
The molar ratio of reactants, moles of OTD and/or MTD to moles of ACN, can vary from about 10:1 to about 1:10. The molar ratio used will affect the rate of reaction and the product distribution, but as the final product is distilled the final product quality is unaffected. To maximize yield and efficiency, the desired molar ratio is from 0.95:1.0 to about 1.0:2.0 with the optimum being about 1.0:1.2.
The cyanoethylation reaction is conducted using at least one acid catalyst. The acid catalyst can be any mineral, carboxylic, super or supported acid, including but not limited to hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, propionic acid, para-toluenesulfonic acid, triflic acid (trifluoromethanesulfonic acid) and Nafion(copyright) super acid catalyst from DuPont, which is a bead-form, strongly acidic resin, i.e., a copolymer of tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octenesulfonyl fluoride, converted to the proton (H+) form. The preferred acid catalysts are hydrochloric acid and Nafion catalyst with Nafion catalyst being most preferred.
Any protic solvent can be used in the cyanoethylation, including but not limited to water, methanol, ethanol, isopropanol, n-propanol, etc.
The cyanoethylation reaction can be conducted over a temperature range from about 50xc2x0 C. to about 150xc2x0 C. within a pressure range from about atmospheric pressure up to about 900 psi (6.21 MPa). The reaction time is dependent on the reaction temperature, pressure and the desired extent of the reaction as measured by gas chromatography (GC). The reaction of TDA with ACN can generate not only a mono-cyanoethylated product (CNTDA) but also a di-cyanoethylated product (DCNTDA). Thus, at any given time during the cyanoethylation there is, for example, a mixture of unreacted TDA, CNTDA and DCNTDA, as described according to the following Equation V: 
The cyanoethylation reaction and products produced thereby are disclosed and claimed in the inventors"" copending U.S. patent application, having the Attorney Docket No. 06231USA, entitled xe2x80x9cCYANOETHYLATED ORTHO AND METATOLUENEDIAMINE COMPOSITIONS AND PROCESS FOR MAKING THEMxe2x80x9d, and filed on even date with the present application.
The cyanoethylated product mixture is converted to crude aminopropylated TDA (APTDA) by catalytic hydrogenation. The product mixture from the cyanoethylation step is carried through to the aminopropylated form, i.e., the unreacted TDA remains in the aminopropylated product mix unaffected, and the CNTDA and DCNTDA are both hydrogenated to the aminopropylated forms APTDA and diaminopropylated TDA (DAPTDA).
When the cyanoethylated product mixture comprises cyanoethylated MTD, hydrogenation not only produces mono- and di-aminopropylated MTD, but also produces the quinolines and di-cyclized byproducts shown below: 
The final composition may contain cyclics ranging from 5 to 50% depending on the fractional distillation conditions employed to purify the product. For example, a typical product mixture comprises about 9% TDA, 16% quinolines, 50% aminopropyl-m-TDA and 16% dicyclic products.
The hydrogenation can be conducted using the product obtained directly from the cyanoethylation or the solvent may be removed. Any solvent known to one skilled in the art can also be used.
The hydrogenation can be conducted over a temperature range from room temperature up to about 200xc2x0 C. Higher temperatures may lead to reforming of the amine mixture and should be avoided. A preferred temperature range is from 50-125xc2x0 C., which permits an adequate temperature differential for good heat removal. The most preferred temperature range is about 100-125xc2x0 C.
The hydrogenation can be conducted at a hydrogen pressure ranging from atmospheric pressure to about 2000 psi (13.79 MPa). Higher or lower pressures may be used without causing a detrimental affect to the product. The ideal hydrogen pressure range is from about 50 to 900 psi (0.34 to 6.21 MPa) with the optimum being 500 to 900 psi (3.45 to 6.21 MPa).
Any hydrogenation catalyst known to be active toward nitrile hydrogenation can be used. Preferred catalysts include Raney nickel and Raney cobalt, with Raney cobalt being most preferred.
The catalyst loading is preferably from 0.01 to 10.0% by weight of the reactant charge, with about 0.5 to about 2.0% being most preferred.
The crude product resulting from the steps above is a mixture of starting TDA, the desired mono-aminopropylated TDA, di-aminopropylated TDA, and where MTD is a reactant, quinolines and di-cyclized byproducts. The composition of the crude product will vary depending on the reaction conditions, catalyst type and reaction time. Typical composition ranges for OTD-based reactions are 20/70/10 to 5/75/20 weight % OTD/mono-APTDA/di-APTDA. Typical composition ranges for MTD-based reactions are 20/15/50/15 to 5/25/45/25 weight % TDA/quinolines/APTDA/dicyclics. Although the crude products are satisfactory as curatives for epoxy resins, it is more desirable to use the purified APTDA. This purification may be accomplished by any method known to one skilled in the art, but the preferable method is reduced pressure fractional distillation, again a method well known to the art. Depending on the distillation conditions and separation capability of the distillation, the purified product from an OTD-based reaction can have an assay ranging from about 90 to 99.9%, with the chief impurities being OTD and di-APTDA (neither of which will impair the performance attributes imparted by this curative to a cured epoxy resin formulation). Depending on the distillation conditions and separation capability of the distillation, the purified product from a MTD-based reaction may have a composition ranging from 1/15/64/15 to 0/12/76/12 TDA/quinolines/APTDA/dicyclics, respectively. However, the compositional possibilities are endless. Again, none of the possible compositions will impair the performance attributes imparted by this curative to a cured epoxy resin formulation.
Use of New Aminopropylated Aromatic Amines in Epoxy Formulations
In addition to being low viscosity, the aminopropylated aromatic amines of the invention provide excellent curatives for ambient and heat-cured epoxy formulations. In ambient-cured epoxies, APTDA provides short gel and thin film set times, not typical of aromatic amines, while providing excellent physical property development such as hardness, gloss and chemical resistance as typically seen with aromatic amine curatives. In heat-cured epoxy formulations, APTDA provides unexpectedly high glass transition temperature (Tg).
The crude, purified and high purity grades of APTDA are mixed thoroughly with an epoxy resin and optionally heated to effect curing. The stoichiometry employed preferably ranges from 0.5 N-H equivalent of the APTDA per equivalent of epoxide moieties in the epoxy resin to 1.5 N-H equivalent of the APTDA per equivalent of epoxide. More preferably, the stoichiometry ranges from 0.9 to 1.1 N-H equivalent per epoxide with a 1.0:1.0 ratio being most preferred.
Any epoxy resin can be employed, including but not limited to the diglycidyl ether of bisphenol A and/or bisphenol F. Solvents such as an alcohol, phenol, aliphatic or aromatic hydrocarbon, esters, ethers and the like can be used. Reactive diluents such as aromatic and aliphatic glycidyl ethers and esters can also be used as well as various types of fillers and colorants.